Goniochromatic luster pigments are described in EP 0 753 545 B2. At least one layer stack comprising a colorless low-index coating and a reflecting, selectively or nonselectively absorbing coating, and also, optionally, an outer protective layer, is applied here to a multiply coated, high-index, nonmetallic, platelet-shaped substrate. The layer thickness of the low-index colorless coating reduces as the number of layer stacks applied to the substrate increases. The goniochromatic luster pigments exhibit an angle-dependent color change between two or more intense interference colors.
In accordance with WO 2004/067645 A2, a transparent substrate is coated with an uneven number—at least three—of layers of high and low refractive index in alternation. The difference in refractive index between the adjacent layers is at least 0.2. At least one of the layers differs in its optical thickness from the others. The resulting multilayer effect pigments therefore do not possess a layer construction in which the optical thickness of each layer is an uneven multiple of a quarter of the light wavelength for interference (no “quarter-wave-stack” construction).
In WO 2006/088759 A1, the multilayer effect pigments are coated with titanium dioxide, with a low-index layer having an optical layer thickness of at least 150 nm, and then again with a high-index layer comprising titanium dioxide, with an optical layer thickness of approximately 45 to 240 nm. The first titanium dioxide layer gives the substrate a silvery luster, whereas the resulting multilayer effect pigments do not possess a silvery luster. On account of the optical layer thickness of the low-index layer, the multilayer effect pigments possess a color flop. Here as well, in the same way as for WO 2004/067645 A2, the adjacent layers have a refractive index difference of at least 0.2. Again, the intention is not to have a layer construction in which the optical thickness of each layer is an uneven multiple of a quarter of the light wavelength for interference (no “quarter-wave-stack” construction).
Multilayer interference pigments with strong interference colors and/or with a strong angular dependency of the interference colors, consisting of a transparent base material coated with alternating layers of metal oxides of low and high refractive index, are described in EP 0 948 572 B1. The difference in the refractive indices is at least 0.1. The number and thickness of the layers are dependent on the desired effect and on the substrate used. Considering the construction TiO2—SiO2—TiO2 on a mica substrate, for example, pigments with a blue interference color are obtained when optically thin TiO2 and SiO2 layers with a layer thickness <100 nm are used, said pigments being more strongly colored than pure TiO2-mica pigments. The incidence of thick SiO2 layers with a layer thickness >100 nm produces pigments having a strongly pronounced angular dependency of the interference color.
JP 07246366 describes an optical interference material which is constructed from alternating layers of high and low refractive index, the optical thickness of each layer being an uneven multiple of a quarter of the light wavelength for interference (“quarter-wave-stack” construction).
Interference pigments based on multiply coated, platelet-shaped substrates which have at least a layer sequence comprising a high-index layer, a low-index colorless layer, a nonabsorbing high-index layer, and optionally an outer protective layer, can be produced in accordance with EP 1 025 168. Between the substrate and the first layer, and/or between the individual layers, there may be further colored or colorless metal oxide layers. The interference pigments may comprise two or more identical or different combinations of layer stacks, but the covering of the substrate with just one layer stack is preferred. In order to intensify the color flop, the interference pigments may comprise up to four layer stacks, but the thickness of all the layers on the substrate ought not to exceed 3 μm.
Multilayer pigments based on glass flakes which are coated with at least three alternating layers of high and low refractive index are described in WO 2003/006558 A2. The glass flakes here possess a thickness of <1 μm. In addition to intense colors, the multilayer pigments exhibit a strong color flop.
WO 2004/055119 A1 describes interference pigments based on coated, platelet-shaped substrates. The substrates in this case are covered with a first layer of SiO2, over which is applied, subsequently, a high-index layer, consisting for example of TiO2, ZrO2, SnO2, Cr2O3, Fe2O3 or Fe3O4, or an interference system comprising alternating high-index and low-index layers. The pigments may optionally also have an outer protective layer. In this way, silver-white interference pigments, or interference pigments with brilliant interference colors, are obtained, which are notable for performance properties, such as mechanical stability and photo stability, but which do not have an extremely high gloss. The color of the interference pigments is not dependent or is only minimally dependent on the angle.
Thermally and mechanically stable effect pigments based on thin glass platelets with a thickness ≦1.0 μm are known from WO 2002/090448 A2. The effect pigments may be covered with one or more high-index and/or low-index layer(s). The glass flakes possess a softening temperature of ≧800° C.
The optical properties of effect pigments can be influenced, according to WO 2006/110359 A2, by a suitable particle size distribution. The glass platelets described here, classified and coated with a single metal oxide layer, have a D10 of at least 9.5 μm, preferably of 9.5 μm. A disadvantage is that the pigments have to have a size range with a D90 of not more than 85 μm, preferably of about 45 μm.